1. Field of the Invention
The present invention pertains to apparatus and methods for manipulating tubular members. More particularly, the present invention relates to well working apparatus for manipulating pipe members into and out of wells.
2. Description of Prior Art
Well working rigs of considerable variety are known, and include design features to achieve special purposes. For example, rigs are known with fold-down masts sufficiently lightweight to be transportable by truck to and from well sites. It is desireable, particularly for economic purposes, to be able to transport virtually an entire rig on a single truck, and to be able to configure the mast for operating on a well in a short period of time after arrival at the well site.
Workover rigs, for performing operations on already-drilled wells are generally small compared to rigs used to initially drill wells and may even take the form of a snubber, a gin pole and a winch line. Such workover rigs are generally transportable by truck. However, such workover rigs may be confined to manipulating a single pipe member at a time as opposed to a drilling rig which can typically manipulate a stand of three pipe members threaded together. Consequently, a workover rig should be operable to manipulate pipe members rapidly so as to minimize the time required to withdraw a pipe string from a well, or to insert a pipe string into a well.
Copending application for U.S. patent application Ser. No. 35,933, filed concurrently herewith, discloses apparatus and methods for manipulating two pipe members by means of two pipe handling devices carried by a Ferris-wheel type double chain assembly. The well working rig disclosed therein includes a foldable mast with motors, for driving the chain, mounted on the masthead.